Iterative Receiver Employing Multiuser Detection and Channel Estimation for MIMO-OFDM IDMA

This paper proposes an iterative receiver employing multiuser detection (MUD) and channel estimation for up-link MIMO-OFDM interleave-division multiple access (IDMA). IDMA can perform low-complexity MUD by employing a low-rate channel code and an individual interleaver for each user, and is expected to improve spectrum efficiency in mobile communications. However, an excellent channel estimator has not been proposed in the uplink MIMO-OFDM IDMA. This paper proposes the iterative receiver that repeats a joint processing of MUD and channel estimation by exploiting log-likelihood ratios of coded bits (bit LLRs) which channel decoders of all users provide. The receiver employs soft decision-directed channel estimation (SDCE) using the bit LLRs during data symbols, in addition to initial channel estimation (ICE) using known preambles. To improve an accuracy of the channel estimation, it performs tap selection (TS) that extracts only dominant paths from a channel impulse response estimated by ICE or SDCE. Moreover, this paper evaluates transmission performances of the proposed receiver, and shows that the receiver can achieve an excellent performance in 4 x 4 MIMO-OFDM IDMA with four users.